Strange... if you store a map for offline viewing in Google Maps, it will be cached for at least a few months - and when that time expires, it will ask you if you want to update it. But I can't vouch for the various hiking apps which may be better for hiking data, but have worse UX overall.

Or you can use an "offline-only" app like OSMAnd and feed it with GPX tracks downloaded from hiking sites, then you only have to worry about keeping your battery charged...